1. Field of the Invention
The present invention relates to a hydrostatic transaxle for a vehicle having first and second axles, the hydrostatic transaxle comprising: a hydraulic pump; a hydraulic motor drivingly connected to the first axle; and a closed circuit fluidly connecting the hydraulic pump to the hydraulic motor, wherein a second hydraulic motor, which is disposed on the outside of the hydrostatic transaxle and drivingly connected to the second axle, can receive power from the hydrostatic transaxle.
2. Related Art
Conventionally, as disclosed in JP 2002-87086 A, there is a well-known four-wheel drive vehicle equipped with a hydrostatic transaxle. The vehicle is provided with a first axle (one of front and rear axles) drivingly connected to a hydraulic motor incorporated in the hydrostatic transaxle. The vehicle is also provided with a second axle (the other of front and rear axles), which is drivingly connected to an output portion of the hydraulic motor through a mechanical transmission linkage including a propeller shaft and a mechanical drive-mode change clutch that is shiftable between a clutch-on position for establishing a four-wheel drive mode and a clutch-off position for establishing a two-wheel drive mode.
Such a conventional hydrostatic transaxle may be provided with a sub-transmission, such as a gear train or a belt transmission, disposed on the downstream of the hydraulic motor. However, the switching of the mechanical clutch accelerates abrasion of components of the sub-transmission, and causes noise and shock.
An alternative conventional vehicle equipped with the above-mentioned hydrostatic transaxle is provided with a second hydraulic motor disposed on the outside of the hydrostatic transaxle so as to drive the second axle, and a fluid passage including at least one pipe is interposed between the hydrostatic transaxle and the second hydraulic motor. In this state, a hydraulic switching valve serving as a drive-mode change valve, which is shiftable between a supply position for supplying fluid to the second hydraulic motor, i.e., for the four-wheel drive mode, and a supply-stop position for stopping the fluid supply to the second hydraulic motor, i.e., for the two-wheel drive mode, has to be disposed on the fluid passage.
Here, the drive-mode change valve is desired to have no exposed fluid pipe such as to complicate the assembling of the hydrostatic transaxle and to reduce efficiency of manufacture of the vehicle. Further, the drive-mode of the vehicle is desired to be automatically changed according to the sub-speed change operation for changing the speed stage of the sub-transmission without requiring the vehicle to be stopped for the drive-mode change operation.